Clinical Usefulness of IgG Food Allergy Testing

William Shaw Ph.D

Immunoglobulin G (IgG) food allergy testing has made vast advancements since the year 2003 when the American Academy of Allergy, Asthma, and Immunology published a statement that "Measurement of specific IgG antibodies to foods is also unproven as a diagnostic tool"(1) Most of the IgG food allergy throughout the world is done using the same immunochemical technique. First, soluble food proteins in solution are reacted to a solid phase that chemically binds to a variety of proteins. The use of plastic microtiter trays with one to several hundred wells has become the most common material used as the solid phase. Then these trays are washed, dried, and stored for later use. A sample of diluted serum is then added to each of the wells. Antibodies of all types in the diluted serum bind to the specific food molecules that are attached to the plastic wells of the tray. Next, the plates are washed to remove any nonspecific antibodies in the diluted serum. At this time, food antibodies from all of the five major immunoglobulin classes called G, A, M, E, and D may be attached to the food antigens on the plate. The next step confers specificity on the assay. Antisera from sheep, goats, rabbits, or other animals that specifically binds to IgG is added to microtiter wells and only binds to IgG, not to IgA, IgM, IgE, or IgD. This antibody to IgG has previously been modified by the attachment of an enzyme that can be measured conveniently. The amount of enzyme bound to food antigen-IgG complexes on the plate is directly related to how much IgG antibody is attached to a given food. The overall technique is termed Enzyme Linked Immuno Assay or ELISA. If IgG4 is measured, an antiserum specific for IgG4 only must be used for the final step.

The clinical usefulness of IgG testing in an array of illnesses is illustrated in an early article published by an otolaryngologist who reported that the majority of his patients had substantial health improvements after an elimination of foods positive by IgG food allergy tests (2). The overall results demonstrated a 71% success rate for all symptoms achieving at least a 75% improvement level. Of particular interest was the group of patients with chronic, disabling symptoms, unresponsive to other intensive treatments. Whereas 70% obtained 75% or more improvement, 20% of these patients obtained 100% relief. Symptoms most commonly improved 75%-100% on the elimination diets included asthma, coughing, ringing in the ears, chronic fatigue, all types of headaches, gas, bloating, diarrhea, skin rash and itching, and nasal congestion. The most common IgG food allergies were cow's milk, garlic, mustard, egg yolk, tea, and chocolate.

The usefulness of IgG food allergy to design customized elimination diets has now been documented in scientific studies. Irritable bowel syndrome (IBS) is a common, costly, and potentially disabling gastrointestinal (GI) disorder characterized by abdominal pain/discomfort with altered bowel habits (e.g., diarrhea, constipation). The major symptoms of IBS are (1) abnormality of bowel movement, (2) reduction in bowel sensitivity thresholds, and (3) psychological abnormality. Many IBS patients have psychological symptoms including depression, anxiety, tension, insomnia, frustration, hypochondria. psychosocial factors (3). Atkinson et al (4)evaluated a total of 150 outpatients with irritable bowel syndrome (IBS) who were randomized to receive, for three months, either a diet excluding all foods to which they had raised IgG antibodies (ELISA test) or a sham diet excluding the same number of foods but not those to which they had antibodies . Patients on the diet dictated by IgG testing had significantly less symptoms than those on the sham diet after 120 days on the diets. Patients who adhered closely to the diet had a marked improvement in symptoms while those with moderate or low adherence to the IgG test dictated diets had poorer response. Similar results were also obtained by Drisko et al (5). They used both elimination diet and probiotic treatment in an open label study of 20 patients with irritable bowel syndrome diagnosed at a medical school gastroenterology department. The most frequent positive serologic IgG antigen-antibody complexes found on the food IgG tests were: baker's yeast, 17 out of 20 (85%); onion mix, 13 out of 20 (65%); pork, 12 out of 20 (60%); peanut 12 out of 20 (60%); corn, 11 out of 20 (55%);wheat, 10 out of 20 (50%); soybean, 10 (50%); carrot, 9 out of 20 (45%); cheddar cheese, 8 out of 20 (40%); egg white, 8 out of 20 (40%). Only 5 out of 20 reacted by IgG antibody production to dairy; however the majority of patients reported eliminating dairy prior to trial enrollment presumably clearing antigen-antibody complexes prior to testing. Significant improvements were seen in stool frequency, pain, and IBS quality of life scores. Imbalances of beneficial flora and dysbiotic flora were identified in 100% of subjects by comprehensive stool analysis. There was a trend to improvement of beneficial flora after treatment but no change in dysbiotic flora. The one-year follow up demonstrated significant continued adherence to the food rotation diet, minimal symptomatic problems with IBS, and perception of control over IBS. The continued use of probiotics was considered less helpful.

IgG food allergy testing was also proved effective in the gastrointestinal disorder Crohn's disease. Bentz et al (6) found that an elimination diet dictated by IgG food allergy testing resulted in a marked reduction of stool frequency in a double blind cross-over study in which the IgG-dictated diet was compared to a sham diet in 40 patients with Crohn's disease. IgG food allergies were significantly elevated compared to normal controls. Cheese and baker's yeast (Saccharomyces cerevisiae) allergies were extremely common with rates of 83% and 84% respectively. Main et al (7), focusing on the baker's yeast allergy, also found extremely high prevalence of IgG allergy in patients with Crohn's disease. Titers of both IgG and IgA to S. cerevisiae in the patients with Crohn's disease were significantly higher than those in the controls. In contrast, antibody titers in the patients with ulcerative colitis were not significantly different from those in the controls. Among the patients with Crohn's disease there was no significant difference in antibody titers between patients with disease of the small or large bowel. Since IgG antibodies to S. cerevisiae cross react with Candida albicans (8), Candida species colonization might be a trigger for the development of Crohn's disease.

IgG food allergy to wheat, gluten, gliadin, rye, and barley are prevalent in the gastrointestinal disorder celiac disease. Virtually all patients with celiac disease have elevated IgG antibodies to gliadin if they currently have wheat or related grains in their diet. The confirmation of celiac disease is confirmed by the presence of flattened mucosa with a lack of villi when a biopsy sample of the small intestine is examined microscopically. Another confirmation test with equal sensitivity is a blood test for IgA transglutaminase antibodies. The antibody confirmation test is equal in accuracy to the biopsy test with the exception that individuals with IgA deficiency may have false negative results. However, I would estimate that only 1% of people with elevated IgG antibodies to gliadin and other grains related to wheat have celiac disease. If the individual is negative for the confirmation tests for celiac disease, many patients are frequently erroneously advised that that have no problem with wheat. Hadjivassiliou et al argued that it is a significant clinical error to classify wheat allergy through the filter of celiac disease (9) and argue that celiac disease is a subtype of wheat sensitivity. Many of their patients with wheat allergy but celiac disease negative had remission of severe neurological illnesses when they adopted a gluten free diet and expressed that in these patients the gluten molecule causes an autoimmune reaction in the brain rather than in the intestinal tract, likely against the Purkinje cells that are predominant in the cerebellum.

Total IgG Versus IgG4 Food Allergy

Immunoglobulin G (IgG) is classified into several subclasses termed 1, 2, 3, and 4. IgGs are composed of two heavy chain–light chain pairs (half-molecules), which are connected via inter–heavy chain disulfide bonds situated in the hinge region (Figure 1). IgG4 antibodies usually represent less than 6% of the total IgG antibodies. IgG4 antibodies differ functionally from other IgG subclasses in their lack of inflammatory activity, which includes a poor ability to induce complement and immune cell activation because of low affinity for C1q (the q fragment of the first component of complement). Consequently, IgG4 has become the preferred subclass for immunotherapy, in which IgG4 antibodies to antigens are increased to reduce severe antigen reactions mediated by IgE. If antigens preferentially react with IgG4 antibodies, the antigens cannot react with IgE antibodies that might cause anaphylaxis or other severe reactions. Thus, IgG4 antibodies are often termed blocking antibodies. Another property of blood-derived IgG4 is its inability to cross-link identical antigens, which is referred to as "functional monovalency". IgG4 antibodies are dynamic molecules that exchange half of the antibody molecule specific for one antigen with a heavy-light chain pair from another molecule specific for a different antigen, resulting in bi-specific antibodies that are unable to form large cross-linked antibodies that bind complement and thus cause subsequent inflammation(16). In specific immunotherapy with allergen in allergic rhinitis, for example, increases in allergen-specific IgG4 levels indeed correlate with improved clinical responses. IgG4 antibodies not only block IgE mediated food allergies but also block the reactions of food antigens with other IgG subclasses, reducing inflammatory reactions caused by the other IgG subclasses of antibodies to food antigens.

In IgG mediated food allergy testing, the goal is to identify foods that are capable of causing inflammation that can trigger a large number of adverse reactions. IgG1, IgG2, and IgG3 all are capable of causing inflammation because these antibodies do not exchange heavy and light chains with other antibodies to form bispecific antibodies. Thus, IgG1, IgG2, and IgG3 antibodies to food antigens can and do form large immune complexes or lattices that fix complement and increase inflammation. The presence of IgG4 antibodies to food antigens indicates the presence of antibodies to foods that will not usually cause inflammation even though high amounts of these antibodies do indicate the presence of immune reactions against food antigens. Testing only for IgG4 antibodies in foods limits the ability of the clinician to determine those foods that are causing significant clinical reactions that are affecting their patients. The importance of measuring other subtypes of IgG antibodies is highlighted in an article by Kemeny et al. (17). They found that IgG1 antibodies to gluten were elevated in all 20 patients with celiac disease but none of the patients had elevated IgG4 antibodies to gluten.

Clinical References

1. Statement of the AAAAI Work Group Report: Current Approach to the Diagnosis and Management of Adverse Reactions to Foods, October 2003. http://www.aaaai.org/ask-the-expert/usefulness-of-measurements-of-IgG-antibody.aspx (Accessed October 27,2013).

14.Vance G. et al. Ovalbumin specific immunoglobulin G and subclass responses through the first five years of life in relation to duration of sensitization and the development of asthma. Clia Exp Allergy 2004;34:1452-1459